The invention relates to investment casting. More particularly, the invention relates to the investment casting of superalloy turbine engine components.
Investment casting is a commonly used technique for forming metallic components having complex geometries. It is commonly used in the fabrication of superalloy gas turbine engine components. In an exemplary casting process, a mold is prepared having one or more cavities, each cavity having a shape corresponding to the part to be cast. An exemplary process for preparing the mold involves the use of one or more wax patterns of the part. The patterns may be formed by molding the wax. The molding may be over sacrificial cores (e.g., ceramic cores) generally corresponding to positives of interior passages within the parts. In a shelling process, a ceramic shell is formed around one or more such patterns. The shelling process may involve dipping the patterns in tanks of coating material (e.g., ceramic slurry). Dry particulate may be applied to the wet coated patterns for enhancing structural integrity and the coating layer may then be dried. The process may be repeated to build up multiple layers.
After the shelling, the wax pattern may be removed such as by melting in an autoclave. The hollow ceramic shell may then be strengthened by applying heat. Molten alloy may then be introduced to the shell to cast the part(s). Upon cooling and solidifying of the alloy, the shell (and core, if any) may be mechanically and/or chemically or otherwise suitably removed from the molded part. The part may then be machined and treated in one or more stages.